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[19:00:12] ERIN BURNETT, CNN ANCHOR: Next, our countdown to CNN's Republican presidential debate tonight. The stakes could not be higher for the four remaining candidates in what could be the most crucial debate so far.

Plus, the breaking news. Sources telling CNN Ben Carson will endorse Donald Trump, a major moment in this campaign, a major boost for Donald Trump with conservatives and evangelical voters. And the most sought after endorsement in this state. My guest tonight, Florida Governor Rick Scott. Let's go OUTFRONT.

Good evening, I'm Erin Burnett. And welcome tonight to a very special edition of OUTFRONT live in Miami. Counting you down to a crucial debate right here on CNN. Donald Trump, Ted Cruz, Marco Rubio, John Kasich, they will all be here in this room, the last four Republicans standing, in their final debate before the winner take all Florida and Ohio. Winner take all. Crucial night. And tonight, the debate leading in. This is the debate stage behind me. This is a huge room. We are going to have a lot of people here tonight. We are the University of Miami. The candidates have been off the trail today behind closed doors getting ready for this debate.

And we are following the major breaking news at this hour. Sources telling CNN, Dr. Ben Carson will endorse Donald Trump at a press conference tomorrow morning. The biggest endorsement for Donald Trump since New Jersey Governor Chris Christie's endorsement last week. He's hoping this will give him a boost among evangelicals. It is a big disappointment for Ted Cruz. It does come though in the shadow of more violence at a Trump rally. This is in North Carolina, what happened was, a black protester was ejected from the event and then sucker punched by a white man in the crowd as you can see there. A pretty shocking and stunning moment.

Now, Trump has promised to tone down the rhetoric. That is something to watch for in tonight's debate. It is a crucial night for Donald Trump. He needs a strong performance, a presidential performance, to deliver, to make good on his promise of what he calls a knockout punch on Tuesday if he wins Ohio and Florida, beating Kasich and Rubio in their home states. Is the race over then? Will it be time for Republicans to coalesce around him? We have it all covered in this hour tonight as we count you down for that debate.

My expert panel will be with me for the entire hour. I want to begin with Jim Acosta though because we have this breaking news. Jim, Ben Carson --

JIM ACOSTA, CNN SENIOR WHITE CORRESPONDENT: That's right.

BURNETT: Going to come in, endorsed Donald Trump. You know, last night on the show I thought it was interesting, he left the door open to endorsing Trump or Cruz, but when I asked him specifically about whether he was upset that Donald Trump had likened him to a child molester, he said, well, I'm not going to judge anyone for a comment made in the heat of the moment, which now seems pretty indicative of where he was going.

ACOSTA: That's right, Erin. And this is outsiders uniting. And keep in mind, you know, there is friction between Dr. Ben Carson and Ted Cruz. Donald Trump likes to talk about this out on the campaign trail all the time. He feels like Ted Cruz was pulling dirty tricks in Iowa to really sort of bounce Ben Carson out of this race and that was to the benefit of Ted Cruz. And so it is not -- I don't think a big surprises to see Donald Trump and Ben Carson joining forces. And as Donald Trump is picking up this very key endorsement, these are desperate times for Marco Rubio on the ropes and in his home state of Florida. Rubio needs a make or break performance to shake up this race before next Tuesday's primary. But Donald Trump is all but labeling Rubio as another piece of campaign roadkill on his path to the nomination.

ACOSTA: At a rally where a protester was sucker punched in the face, Trump also brushed off the latest surge from Ted Cruz as two little too late.

TRUMP: Lying Ted Cruz came up but he said, I'm the only one that can beat Donald Trump. He doesn't know how to win.

ACOSTA: But hold on, in Florida, a state well-known for its wild outcomes, the attack ads are flying fast. From this anti-Trump Super PAC spot featuring a man who says he worked as a salesman from Trump University --

UNIDENTIFIED MALE: With Donald Trump you always have to read the fine print.

ACOSTA: -- to this Trump ad slamming Rubio for his controversial Florida connections. UNIDENTIFIED MALE: When Marco Rubio became Speaker of the House, he

brought his friends along for the ride.

ACOSTA: Even as Trump is expecting a less combative debate performance from Rubio.

TRUMP: I think it's going to be softer, but I'll be ready. I mean, you know, I think that Marco is going to be a different person.

ACOSTA: Rubio who is fighting for his political life is seeing his ground game tested. His campaign lined up this football stadium for a rally last night, but drew a crowd that was far smaller than the venue's capacity. But Rubio's adviser say, the Florida's senator will still be aggressive hitting Trump on his business record rather than the size of his hands.

[19:05:14] SEN. MARCO RUBIO (R-FL), PRESIDENTIAL CANDIDATE: At the end of the day, you know, it's not something I'm entirely proud of. My kids were embarrassed by it, and you know, if I had to do it again, I wouldn't.

ACOSTA: Cruz has his own lines of attack ready for Trump. He's accusing him of manipulating his supporters.

SEN. TED CRUZ (R-TX), PRESIDENTIAL CANDIDATE: Donald gave a press conference here he said, to quote him, "I love the poorly educated." Listen, part of it is, I think Donald is taking advantage of his voters.

ACOSTA: And Florida is hardly the only battleground. John Kasich rising in the polls in his home state of Ohio.

GOV. JOHN KASICH (R-OH), PRESIDENTIAL CANDIDATE: I'm going to be the Republican nominee.

ACOSTA: Trump is suddenly attacking him.

TRUMP: We have Ohio where you have an absentee governor. We'll do great, great, great in Ohio.

(END VIDEO CLIP)

ACOSTA: Now, Trump's campaign manager Corey Lewandowski tells me he is expecting Rubio to go on attack at tonight's debate. It's no secret Trump is looking for a double knockout punch next week as he hopes to take out Rubio in Florida and Kasich in Ohio. If that happens, one top GOP told me, Trump is their nominee and it doesn't hurt, Erin, for Donald Trump to have the endorsement of Dr. Ben Carson. Just part of the fruit salad of this campaign -- Erin.

All right. Let's go to Sunlen Serfaty, she is also here in this debate hall with me where the Republicans are going to be facing off in just moments. And the breaking news of course Ben Carson going to endorse Donald Trump tomorrow morning. Sunlen, what are you hearing?

SUNLEN SERFATY, CNN CORRESPONDENT: Well, it's interesting, Erin. The view that we're getting from the Cruz campaign is that Senator Cruz is going to be trying to distinguish himself tonight up here on the debate stage in his tone and in his approach. A Cruz campaign official says not Cruz is preparing a big economic message tonight that he will be trying to speak directly to voters about the issues that they are facing. Their plan is really not get engaged in the mudslinging, try to look a little presidential up there on the debate stage, and really speak to the issues that voters are facing.

You know, so much has been said about Marco Rubio facing high stakes and John Kasich facing high stakes, but the Cruz campaign really sees a big potential to stand out tonight up there on that debate stage to distinguish himself from the other candidates and to present himself as the most viable alternative to Donald Trump. The Cruz campaign really sees tonight as an opportunity to inch towards that goal -- Erin.

BURNETT: Sunlen, thank you.

And OUTFRONT now, our senior political reporter Nia-Malika Henderson. Adam Smith also with me. The Tampa Bay Times, a political editor with the paper since 1992, news more about this state than anybody. Gloria Borger also with me. A former president to Trump Productions, Andy Dean. A Donald Trump supporter with me. Political commentators S.E. Cupp, and Ben Ferguson also here.

OK. Let's start with this breaking news. Gloria, Ben Carson. Most recent polling early March, six percent of voters. So maybe not that high. But still a loyal, loyal group of voters. He raised an incredible amount of money from individual donations. How significant is the Ben Carson endorsement for Donald Trump?

GLORIA BORGER, CNN CHIEF POLITICAL ANALYST: Look, I don't think it's going to bring huge numbers to Donald Trump because he didn't have that much support but in many ways, Carson's supporters were as loyal to him as Trump supporters are to him. And so, if Carson endorses which he will do tomorrow morning, it seems to me that his voters may follow. So, if I were Donald Trump, I would welcome this with open arms. And it's really not a surprise that he's not going after endorsing Cruz as we were saying before because they had this whole question about whether Cruz played some dirty tricks on him in Iowa.

BURNETT: Right. Even though Donald Trump said that Ben Carson behaved like a child moles molester. I mean, I'm just saying it wasn't --

BURNETT: Yes. SMITH: I think it might have been more surprising if he endorsed Cruz.

BURNETT: Right. Right.

SMITH: Carson actually lives in Florida, but he's retiree. He's not that well-known. But I'm just struck by their occasional moments when you say something -- remember when he called him a child molester? Like, this is actually happening. What planet are we on that candidates are calling each other child molesters?

BURNETT: Yes. Well, it's shocking. I want to also talk about the video which has showed you briefly at the top of the show. This is a video at a Trump rally yesterday. The person who punched this protester has now been booked. But I want to play it again so everybody can see it. You had a protester being escorted out. And then he was sucker punched. The protester was black. The man who punched him in the face who has now been booked as you can see is, you know, white. Now, that's how it happens to be.

S.E., the issue here though is, does Donald Trump need to say more? Does he need to do more? This is not the first time that we have seen violence at a Donald Trump rally.

[19:10:01] S.E. CUPP, CNN POLITICAL COMMENTATOR: Donald Trump I think gives sort of a nod and a wink to this sort of thing when he talks at his rallies about protesters. Get them out. Get them out. You know, in the good ole days we would have knocked them out. I wish I could knock them out. I'd punched him out. He'd said that. Now, Donald Trump is not entirely responsible for what this lunatic guy did at a rally, but it should be up to Donald Trump to set the tone just as it would be up to Donald Trump to set the tone of an administration. And his rhetoric throughout this entire campaign has set exactly that kind of tone.

BURNETT: So, Andy, what does Donald Trump need to do tonight though, because you have said he needs to have a new tone, he needs to be presidential? Is he going to do that tonight or when someone throws the bait out, which they will, is he going to take it?

ANDY DEAN, FORMER PRESIDENT, TRUMP PRODUCTIONS LLC: Oh, he's going to fight back, but we have to get to this point that you see a protests -- not a protests -- somebody protesting at a Trump rally and then he gets hit. I mean, you got understand the context here. And anybody watching at home gets this if they have any common sense. There are 20,000 people coming to these rallies. Sometimes 40,000 people coming to see Donald Trump. Anytime there's 40,000 people in a venue whether you get to a concert or supporting event --

BURNETT: Someone gets punched in the face?

DEAN: Somebody gets punched.

BEN FERGUSON, CNN POLITICAL COMMENTATOR: Not a political rallies. That is not true. Political rallies.

DEAN: Ben, how about this though --

(CROSSTALK)

FERGUSON: On top of having a candidate in Donald Trump who stands out there and says, I'm not going to disavow the KKK, I wish I could punch that guy out, and then he says, about an African-American candidate that he looks like he's acting like a child molester in Ben Carson -- and then you have a White guy hitting an African-American guy. And you actually had some people that actually enjoyed it. And Donald Trump is the guy --

CUPP: And congratulated him for it.

FERGUSON: Yes. Exactly.

DEAN: He was a 78-year-old guy. And I was just saying, it's amazing that he could throw a punch. But the violence is unacceptable. Ben, the issue with this --

(CROSSTALK)

Ben, calm down for a second. Donald Trump rallies. Once again, they're 20, 30,000 people. Liberals go in at a Donald Trump rally. He never seen a full hour. Maybe they show ten minutes on TV. OK. Fifteen to 20 times throughout that rally there will be a protester. Usually it's a college kid that is a hippy.

FERGUSON: That's what happens when you ran for president and you don't but not somebody else.

DEAN: You notice that Hillary Clinton, you don't have conservatives going on.

BURNETT: But Andy, this isn't happening in anybody else' rally?

DEAN: Correct. That's to show that --

BURNETT: And you're saying it is just a matter of numbers?

DEAN: No, no, it's not a matter of numbers. I'm saying, far left liberals go in and they're more disrespectful. You don't see conservatives go in and go, hey, Hillary, blah, blah, blah, 15 times in one of her rallies.

BURNETT: But are you saying that this guy -- the White man who punched the Black man in the face is a White liberal?

DEAN: No, no, no, no. I'm saying, Liberals going to Trump rallies to try to create chaos. You don't see conservatives going to Hillary Clinton's rallies and creating chaos. That's my point. The fact that what their skin color is, we can make a determination. We don't know what happened there.

FERGUSON: If you know this is going to happen at a Trump rally and you do, you're saying it happens every rally.

DEAN: Yes. And mostly --

FERGUSON: Then why not make sure that your supporters when you're running for president and make it clear that you're not going to advocate punching someone in the face.

DEAN: Correct. Trump says no violence. That's simple.

(CROSSTALK)

BURNETT: But tonight how important is it for Donald Trump to set a tone that he is going to elevate the conversation instead of being the one that jumps at the opportunity to bring it down?

NIA-MALIKA HENDERSON, CNN SENIOR POLITICAL REPORTER: No. I think that's been important throughout this entire campaign and you've seen him at times try to do that, but then he sort of gets back to the old Trump who can't seem to not take the bait if it is thrown his way. And he usually kind of lapses back to the Trump that we know that likes to, you know, throw punches and get in the mud with other people, but it is at a different point in this campaign now. He needs to be more presidential, he needs to be more statesman like. He is a guy who was at this point saying, listen, Republican Party unify around me. So, I think it is important that he sets a different kind of tone.

BORGER: Do you remember John McCain when he had a town hall and he had somebody at a town hall come up and say, you know what? President Obama is a Muslim and, you know, McCain said stop, he's not. I don't want to hear that. And that was a moment for McCain that was presidential. And I remember at the time thinking, you know what, this person is a supporter of his. And he said to this person, you know what? Stop. And I think it's an opportunity for Trump to say, you know what, I love your passion, I love your enthusiasm, but this is not what we do.

BURNETT: And that is why the stakes are so very, very high tonight. You're all going to be with us.

DEAN: OK.

BURNETT: Don't go anywhere.

OUTFRONT next, Donald Trump the polls. He is polling very strongly here in Florida and in some polls in Ohio as well. A little tighter there. The question is, did anyone stop him? My guest, RNC Chairman Reince Priebus is going to be with me right after this.

Plus, the Governor of Florida Rick Scott also OUTFRONT tonight. Why isn't he backing his own state Senator Marco Rubio for the nomination? And Hillary Clinton taking new shots at Donald Trump. Why she says he can't beat her. We're counting you down to tonight's CNN GOP debate. And this race got even more exciting tonight with that breaking news of Dr. Carson about to endorse Donald Trump.

(COMMERCIAL BREAK) [19:18:37] BURNETT: Welcome back. We are live tonight at the University of Miami here in Florida where the four remaining Republican candidates will face off right behind me. Podiums are all ready to go. It is a crucial prime time debate that you will see right here on CNN. Where's the little more than an hour away from the major event. Breaking news on the trail tonight. Sources telling CNN Ben Carson will endorse Donald Trump. This development plus a win tonight at the debate could fuel his growing momentum. For Marco Rubio and John Kasich this could be do or die before next week's winner take all primaries which of course are in their home states. Florida here for Rubio and Ohio for Kasich. Contest Donald Trump says he will win and that it will win him the nomination.

(BEGIN VIDEO CLIP)

TRUMP: If I win Ohio and if I win Florida, you're going to be pretty much assured of doing that.

ANDERSON COOPER, CNN ANCHOR: You think you're going to get all the delegates?

TRUMP: I think so. Yes. I really think so. I don't see the convention going that round. I see probably getting the delegates. You know, it's like the fighters. That's the ultimate way of doing it. You'll not come out. If you'll not come out, nothing can happen.

(END VIDEO CLIP)

OUTFRONT now, Republican National Committee Chairman Reince Priebus. Good to have you with me. Chairman, I appreciate it.

I want to start with the breaking news. Dr. Carson coming out endorsing Donald Trump announcing it formally tomorrow morning. Donald Trump yet again going to own a news cycle no matter what happens at tonight's debate.

REINCE PRIEBUS, CHAIRMAN, REPUBLICAN NATIONAL COMMITTEE: I mean, that's what you guys are reporting. I don't know what the details are of that. But you know, look, Dr. Carson has done a great job. I mean, expanding our party. He's an important voice in our party. He's good man. But I don't know the details of it. But certainly there are a lot of endorsements going on around the country right now. And if it's true, that's a big gift.

BURNETT: It certainly is a big gift. Ted Cruz would have won it. Everybody would have won it.

BURNETT: All right. If Donald Trump wins Florida and Ohio, you've got to admit it's going to become incredibly difficult for someone else to win the nomination, isn't it?

PRIEBUS: Well, you know, I'm not in a position to really start, you know, talking about where everyone's delegate math is going. But obviously, whoever gets the majority of delegates, we're going to be behind that nominee 100 percent. But if you have to get to 1237. So, it will be sometime before someone gets the 1237.

BURNETT: OK. So, what you just said there I want to make sure I really understand.

PRIEBUS: Sure.

BURNETT: You said and then you said 1237.

PRIEBUS: Right.

BURNETT: But somebody could have the majority of delegates and not have 1237 which of course is the formal number. So, are you saying if someone has the majority, but not 1237 you'll still support them? They would be the party nominee?

PRIEBUS: Well, you have to have the majority of delegates. Either as a presumptive nominee which is 1237. If you don't have the 1237, you can't be presumptive nominee. I mean, there are certain things we can do by law that were regulated by the Federal Election Commission. I mean, this is not like, people talked about this stuff as if it's just some sort of loss fabric and if I feel like supporting someone, then that's what will happen. There are actually laws that regulate our involvement. So, if we have a presumptive nominee of our party, we can join in with that presumptive nominee. We can spend certain money at the RNC with the presumptive nominee before they actually get formally nominated on the floor of the convention. If a person doesn't have or doesn't look like they're going to get to 1237, then we have to wait until we get to the convention.

BURNETT: All right. So, then -- majority you would still have to get to the convention before you would actually say, OK, you're my main at this point.

PRIEBUS: Right. That's right. All right. So, you know, last night, when I was talking to Ben Carson, he said he was embarrassed by the last debate, as an American, as a Republican debate, he was embarrassed. You said you want the tone of the campaign to improve. Just to embarrass you, but to remind our viewers, let me play the tone we have all experienced. Here we go. Yes.

(BEGIN VIDEO CLIP)

TRUMP: She said I never expect to hear that from you again. She said he's (bleep). That's terrible. Terrible.

RUBIO: Have you seen his hands? They're like this. And you know what they say about men with small hands.

TRUMP: Everything that's been involved in Hillary has been lawsuits. You take a look. Even a race to Obama she was favored to win and she got schlonged. She lost.

CRUZ: I don't really have any views on the size of any parts of Donald Trump's anatomy. And I'm not interested in talking about that. (END VIDEO CLIP)

BURNETT: You cringe, you laugh, it's mortifying in many ways. I know you have talked to most of the candidates specifically about their tone. Were they receptive? Are they going to change?

PRIEBUS: Well, no, I think if you look at what the campaigns are saying, they all agree that the last debate probably was not the best picture, I think, for our debates. And as I've said over the weekend and this week, I want to get a pg or a "g" rating here tonight. I'd prefer a "g" rating, but, you know, I just point out, settle for pg. I think you're going to see that though. I actually think and obviously I'm on CNN and I'm not just saying. But I think Jake, I think CNN is also doing a great job in making sure that some steps are also taking the kind of cool the temperature on the debate stage, which is really important.

[19:23:43] BURNETT: President Obama has been -- some people has said, he is the one to blame for what's happening. There are people who have been saying that. Republicans. He responded to that today and here's what he said.

(BEGIN VIDEO CLIP)

PRES. BARACK OBAMA (D), UNITED STATES: I have been blamed by Republicans for a lot of things. But being blamed for their primaries and who they're selecting for their party is novel.

(END VIDEO CLIP)

BURNETT: Is the civil war that your party is going through right now, his fault?

PRIEBUS: I don't know about a civil war. I mean, I think that both parties are having a pretty big debate right now about the direction of party, but no. I think that people are frustrated with things not getting done in Washington, D.C. People are frustrated with an economy that's not better off. He does have a lot to answer for in regard to the promises he's made and what he's delivered. I mean, he has a lot of things to answer for in his own party. I mean, you look at Michigan where, you know, Bernie Sanders came in and he wasn't supposed to win big, diverse states in this country and he did.

So, you know, look, I think there's a lot of frustration out there, but I also think there's a tremendous participation. We have 70 percent more participation in our party than ever before in our party. That means something. So, we are actually crushing the Democrats. Now, yes, we do have to unify. We do have to come together. It's hard sometimes to come together, but we will because Hillary Clinton will bring this country further in the ditch. Her numbers are already in the ditch. So, I think that we'll do well.

BURNETT: All right. Reince Priebus, thank you very much.

PRIEBUS: Thank you.

BURNETT: A big night for your four candidates tonight. We'll see if they can keep it, G-rated.

OUTFRONT next, you are looking at live pictures of Bernie Sanders about to speak to a huge crowd here in Florida, in Tampa as it happens to be. Hillary Clinton says, she is ready to fight him to the very end.

[19:29:40] BURNETT: Welcome back from Miami. We are just about an hour away from the CNN Republican debate. It could be a game changer in this campaign. On the Democratic side, Bernie Sanders is speaking live at this moment. Also in Florida at a crucial primary here. It's at a rally in Tampa across the state. Sanders looking to pull off another major upset while Hillary Clinton says today, she is prepared to fight all the way to the Democratic convention.

[19:30:02] Jeff Zeleny is OUTFRONT.

(BEGIN VIDEOTAPE)

JEFF ZELENY, CNN SENIOR WASHINGTON CORRESPONDENT (voice-over): It's a Democratic fight with no end in sight.

SEN. BERNIE SANDERS (I-VT), PRESIDENTIAL CANDIDATE: The American people are angry and they have reason to be angry.

HILLARY CLINTON (D), PRESIDENTIAL CANDIDATE: I don't think you move into the future by fighting about things that happened 20 and 30 years ago.

ZELENY: At least not before June when the primary calendar ends. We caught up with Hillary Clinton today campaigning in Tampa.

(on camera): Can you understand why Senator Sanders wants to stay in this race until the very end, until California?

CLINTON: Well, I stayed in the race until the very end. Look, I think everyone has to run his or her own campaign. I respect that. If we go to the end, we go to the end, just as I did in '08.

ZELENY (voice-over): The fireworks in the debate stage in Miami on Wednesday night, some of the loudest and most explosive yet between the Democrat rivals, signaled a rough and rocky road ahead.

SANDERS: No, I do not support vigilantes. That is a horrific statement, an unfair statement. CLINTON: Senator Sanders is always criticizing the recent Democratic

presidents. But I wish he would criticize and join me in criticizing George W. Bush who I think wrecked the economy.

SANDERS: I gather Secretary Clinton hasn't listened to too many of the speeches.

ZELENY: The escalating tension between Clinton and Bernie Sanders, who are getting under each other's skin and hitting the campaign trail hard, with five more states voting in five more days.

SANDERS: If you come out and your friends and family and neighbors come out, we are going to win here in Florida.

ZELENY: If it's Trump, Clinton told us his record may not be as impressive as he thinks.

CLINTON: Look, as I said, I've gotten more votes than he has. I think he has really analyzed a pretty narrow base. Let's find out. If he gets nominated, we're going to have a very vigorous general election if I'm the nominee.

ZELENY (on camera): Is he still yet to be defined, though? I mean, this has been a primary campaign.

CLINTON: We'll wait and find out.

(END VIDEOTAPE)

ZELENY: But many Democrats are not waiting to find out. Even as Hillary Clinton has to take on Bernie Sanders who is drawing big crowds today in Florida, some 5,000 people outside of Orlando. The Clinton campaign and the Democratic machine is starting to focus on Donald Trump, who they do believe will be the Republican nominee. They're looking at his business dealings, other things, seeing how they would define him in some of these battleground states.

And, Erin, interestingly, these primaries that are coming up now and happening now are indeed happening in general election battlegrounds. Here in Florida, also in Ohio, also possibly Illinois and Michigan, if Donald Trump would put these states into play.

That's why this next stretch here, this next five days or so, so interesting to watch on both sides of the race because they are so, so, so interconnected -- Erin.

So, Adam, obviously looking, you know, prohibitively strong here in Florida, but it is not winner-take-all for the Democrats, as you were explaining. So, how well could Bernie Sanders do here? ADAM SMITH, POLITICAL; EDITOR, THE TAMPA BAY TIMES: You know, he's

way behind. This is really the first time this entire cycle he's really set foot in Florida to do anything, but, you know, he's got a fair amount of passionate support. So, if he wins 30 percent or 40 percent, it's not a blowout, but it is still a fair number of delegates.

BURNETT: So, he could still add to his delegate count, which is the crucial thing that keeps this alive, Ron.

RON BROWNSTEIN, CNN SENIOR POLITICAL ANALYST: Well, look, I mean, the way the Democratic proportionality works, two things are true. It is hard to knock someone out completely and it is hard to catch up when you're behind. I mean, both things are true.

Hillary Clinton's delegate lead is, you know, a fact, especially compounded by her advantage among the super delegates. That doesn't mean there are not reasons for Bernie sanders to stay in the race, but he needs a change in the fundamental dynamic to overtake her between now and the end of the line.

NIA-MALIKA HENDERSON, CNN SENIOR POLITICAL REPORTER: You know, I think you've got to win something like 60, 65 percent of the remaining delegates to overtake her lead and her lead is bigger than Obama's ever was in 2008. I think one of the things to watch going into Tuesday is how she does with white voters, because she really got beat by white voters in Michigan. That was the big game changer. You saw Bernie Sanders eat into her lead, those blowout leads she had down south. It'll be interesting to see if that's something he can transfer to these different states, Florida, Illinois, North Carolina.

BURNETT: Which is an interesting point, because, Ed, when you look at the African-American percentage of the population, Florida, about 30 percent, similar to Michigan, the states where Hillary Clinton has delivered her blowout victories, had a vast majority of the Democratic voters being African-American. It is different here. It is more like Michigan in that one demographic regard.

ED O'KEEFE, THE WASHINGTON POST: It is. But if you look at the survey, the poll that we did with Univision this week, she has a lead 72 percent to 16 percent among non-white voters.

[19:35:07] I don't see how he makes that up in any significant way that will chip away. I mean, they're thrilled about the fact that he did better among young black voters in Michigan. That he won the Muslim American vote in Michigan. It won't happen here.

It won't happen here for a lot of reasons. Last night, he probably damaged himself a bit with any Hispanics or Cuban American voters who might have been thinking about it by merely wavering on questions about the Castro regime. They played that clip of him last night 20 years ago sort of defending the Castro regime had done, there were people booing into the hall who were cheering him on for student debt and other issues. And they heard that, and they realize it's a nonstarter. BROWNSTEIN: You know, Erin, if you look toward next Tuesday, you'd have to say that Ohio and Missouri are probably the best shots of Bernie Sanders. Demographically similar to Michigan, even more so, smaller African-American population, but also receptive to the trade message, Rust Belt kind of state. If you look at Illinois, Florida, and North Carolina, more diverse, more challenging.

HENDERSON: Yes, I think that's significant. In the south, not really a big labor movement in the south, and that's in some ways why I think Bernie Sanders wasn't able to catch on with African-Americans or white voters, but as Ron said, I think up north, not only northern whites but northern blacks, more prime to that sort of progressive labor movement.

SMITH: The biggest stronghold in Florida is Miami-Dade. And some Democrats love the idea of political revolution. Around here, that's a scary word.

BURNETT: You know, it's interesting. Bernie Sanders, we were just having a conversation about the supporter at a Trump rally who -- protester was being escorted out, a black protester, the white supporter man sucker punched him, a horrible incident.

Bernie Sanders has just addressed this actually at his rally and what he said is, "No one in America should ever fear for their safety at a political rally. This ugly incident confirms that the politics of division has no place in our country. Mr. Trump should take responsibility for addressing his supporters' violent actions."

Will he do that tonight?

BROWNSTEIN: He's done the opposite so far, right? I mean, he's had several comments at rallies where he's talked about in the old days, they would carry him out on a stretcher. He seems to have tolerated, if not welcomed, the kind of physical response to the protest. I think it is very important to see what he says tonight.

As part of this sort of general divergence we are seeing with Trump, on the one hand, he is rolling towards the nomination. I mean, he's clearly stronger in any of these other candidates. On the other hand, every warning light on the dashboard is blinking red at the moment for him as a general election candidate. NBC/"Wall Street Journal" reported today the worst favorable/unfavorable they've ever tested in a presidential primary candidate.

So, you've got in Trump someone who has done a lot of things that have really energized the portion of the Republican coalition, but have also worried and even frighten voters beyond that coalition.

HENDERSON: Yes, and particularly women. I mean, if you look at the gap he has with women voters compared to Hillary Clinton, he's losing women by something like 20 points. There was a "Politico" story that says he's got to get 7 in 10 white men, something that's never happened before, to win this thing.

So, they have to figure out. I think he's got to figure out if he can broaden his base. Incidents like this don't help.

BURNETT: All right. Thanks very much to all of you. And just -- we've got a live picture here as we -- Marco Rubio right here outside the University of Miami where we are sitting right outside this room arriving for tonight's debate. Obviously this is a crucial, crucial moment for Marco Rubio in his home state. Looks like his wife Jeannette is with him, getting ready to walk in here as candidates are arriving for this crucial debate.

OUTFRONT next, the man with the most coveted endorsement in the state of Florida, Governor Rick Scott, will be my guest right here at the University of Miami as we count you down to the Republican debate. The four remaining candidates will be going head to head kicking off in less than an hour.

(COMMERCIAL BREAK)

[19:42:40] BURNETT: Welcome back.

We're counting you down to tonight's CNN's crucial Republican debate moderated by my colleague Jake Tapper right here at the University of Miami. It begins at 8:30 Eastern, right in this room, with just days to go until this state's game changing winner-take-all Republican primary.

The candidates are all trying to secure one of the most sought after endorsements, that is the Florida Governor Rick Scott.

He's with me OUTFRONT tonight.

GOV. RICK SCOTT (R), FLORIDA: It's exciting here in Florida, right? All these billionaires are moving here and then they spend all their money running ads.

BURNETT: All their money running ads against Donald Trump, who you have said is a friend of yours.

SCOTT: He's a very good friend. Senator Rubio is a very good friend. He got elected senator when I got elected as governor. John Kasich has been governor when I've been governor. So, we deal with the same issues. Most of them are Barack Obama issues.

Ted Cruz I don't know as well, but I compete with his state all the time for jobs.

BURNETT: And here's the thing though -- so, Marco Rubio, you know, he is your senator. He campaigned for you. Donald Trump is a friend of yours. You wrote an op-ed actually in "USA Today", in which you talked very positively of Donald Trump. You said, "I know him personally. There's no doubt he tweets and speaks his mind freely, but I don't think his ability to give the most interesting interviews or speeches is the only thing that has him leading in the polls. I think he is capturing the frustration of many in America."

Dr. Ben Carson just endorsed him. What's holding you back? SCOTT: Well, if you go back to my race in 2010, I was not the

establishment candidate. I was a business person and outsider. The Republican establishment was completely against me. They had their person.

I listen to the voters, and I'm going to do the same thing with this. I'm going to wait and listen to the Republican voters. I think it's going to be about jobs. I won in 2010 and 2014 by talking about job creation. It's the most important issue.

BURNETT: So, it sounds to me like you basically have endorsed Donald Trump, but you haven't done it. You're not going to do anything formally until after voters in Florida vote.

SCOTT: I'm not going to do anything until Tuesday, but I think it will come down to who voters believe will get our country back to work.

BURNETT: So, Donald Trump has had some incidents, violence at his rallies and the incident that is getting a lot of discussion tonight happened last night. There was a protester getting escorted out, African-American. Got sucker punched by a white attendee at the rally.

Should Donald Trump specifically denounce this? He's sort of made jokes about it. When these protesters come to his rally, he said, I used to want to carry them out on a stretcher. Now I just said get them out. Get them out. It's become one of his bits.

If you stop and think about it, people want to be safe. They want jobs. They want a good education system. It's the most important thing. I don't know what happened in those cases, but I know I don't want any violence to happen in our state. I don't think anybody wants any violence in this country.

BURNETT: But in terms of Donald Trump, does he need to say more, that this is not OK?

SCOTT: Well, I think that's up to Donald Trump. I know that when I ran, I didn't want anything to happen to anybody. I wanted people to come to my events. I wanted them to feel safe because I want them to keep coming back to my events and vote for me eventually.

BURNETT: So, Donald Trump made some comments to CNN last night, as you know. He has said that he would ban non-American Muslims temporarily from entering this country until he revamps the entry system. He was asked about the religion of Islam last night here on CNN and here's what he said.

SCOTT: Well, we're sitting in Miami. I was at a funeral two years ago for a journalist Steven Sotloff who was beheaded by radical Islamists. There are people who clearly hate America. There are people that love America.

But it's not surprise that radical Islam does not like our country. But when I think about this I think about what's happened to people like Steven Sotloff.

BURNETT: He had to be asked several times until finally Anderson Cooper asked him, do you mean radical Islam? And he said yes. He didn't take at the beginning.

And part of that -- it's comments like those that are causing some to compare him to Hitler, people who do not like him. The current president of Mexico, the former president of Mexico, have compared him to Hitler. Vicente Fox, former president, specifically said, quote, "He reminds me of Hitler. It's direct. It's not an illusion. It's a direct thing. He reminds me of Hitler."

Do they have a point?

SCOTT: Well, I'm not sure exactly what Donald meant when he said. I can tell you what happened after the Paris attacks, what I said is until the federal government can make us comfortable with our vetting process is, I don't want anymore Syrian refugees to come in my state, because as we know in Paris, we had one of the terrorists has posed as a Syrian refugee.

BURNETT: Right.

SCOTT: We've got to make our country feel safe about, you know, people that are coming in and they're vetted, and we know who's coming to our country.

BURNETT: Just to be clear, though, supporting not having refugees come into Florida is different than temporarily supporting a ban on all Muslims. Would you support that?

SCOTT: Well, I would support is -- I want to understand the vetting process. I asked the White House on a call, tell me how the vetting process is better than the French vetting process? I'm sure the French government wants their citizens to be safe. They couldn't tell me.

I asked them, will you give my law enforcement the same information you have on their backgrounds of these refugees? They said no. That's wrong.

We should know what the vetting process. And our law enforcement should know, if they're going to send Syrian refugees into our state, exactly what their background is.

BURNETT: Governor Scott, thank you very much. Appreciate your time.

SCOTT: Have fun tonight.

BURNETT: The governor of Florida here in Miami with me.

OUTFRONT next, we're a little over 30 minutes away from the CNN Republican debate. It could be the most decisive of the race so far.

When we return, the keys to tonight's showdown.

(COMMERCIAL BREAK)

[19:52:10] BURNETT: Welcome back.

We are live at the University of Miami for tonight's crucial Republican debate. CNN anchor Jake Tapper getting ready to moderate and he will be joined by our Dana Bash, Salem talk radio host Hugh Hewitt and "The Washington Times", Stephen Dinan.

My panel is back with me. And also joining me, CNN political commentator, former communications director for Ted Cruz, Amanda Carpenter.

Let's go around, everybody. This is a very big night. Do or die for Marco Rubio. Crucial for Kasich. Crucial for Donald Trump because he's got to show he can deliver the statesman-like goods. Crucial for Ted Cruz to show he can beat Donald Trump.

What are you looking for?

HENDERSON: Yes, I want to see the Kasich-Trump dynamic, if there is one. Trump has been in Ohio, slamming Kasich as the absentee governor. Does he bring that tonight, and how does Kasich respond? Does he continue to try to rise above it, be Mr. Rogers, Mr. Nice guy or get a little down and dirty?

BROWNSTEIN: John Kasich's neighborhood?

HENDERSON: Yes.

BROWNSTEIN: I think that the key tonight is whether John Kasich and Marco Rubio in particular can make the case to their home state voters that this is the do or die moment. This is larger than about how you feel about me. This is about whether or not you want Donald Trump as a representative of the Republican Party, because if he wins one or certainly both of those states, it is going to be almost impossible to stop him.

AMANDA CARPENTER, CNN POLITICAL COMMENTATOR: And I would say Ted Cruz needs to make everyone in this room forget about Marco Rubio and John Kasich and convince people it's a Cruz/Trump race and he is a consensus conservative candidate who can win.

ANDY DEAN, DONALD TRUMP SUPPORTER: I think it's not going to be so much what is said but how it's said, because we've heard all this stuff before. Is Donald going to act presidential and classy? And when he does get attacked because we expect that to happen, can he do so in a tough way and show he's not weak but tone it down a little bit?

BURNETT: But not be personal or vindictive in any way.

DEAN: Personal to him. But he's on the precipice on Tuesday of becoming the Republican nominee for the presidency of the United States. So, I think he wants everybody to come together and for everybody to come together, a little less of the personal stuff.

S.E. CUPP, CNN POLITICAL COMMENTATOR: I'm less on the edge of my seat about whether Donald Trump will be presidential tonight. I don't expect he will sound presidential and also, it's a low bar for him. I expect that he will get swung at, and he'll return fire as per usual. So, I am not holding out hope that this I like a different tone, like a new Trump debate.

But I am looking at Marco Rubio tonight. Can he speak directly to Floridians in his home state and remind them of what he means to them and how high the stakes are for Florida voters in this coming election?

He's got to have his best debate performance, ever. I know he's capable of it. We've seen him have good nights. He just needs to -- he needs to deliver.

BEN FERGUSON, CNN POLITICAL COMMENTATOR: I think it's going to be interesting to see specifically from Ted Cruz, can he show the country this is a two-man race?

[19:55:02] You are going to have two others basically saying, look at me in Florida and look at me in Ohio. We're still here, but Ted Cruz needs to walk out there and make it very clear this is a two-man race.

For Donald Trump, will he act presidential tonight? I think the bar is so low at this point, he's going to do just fine at being Donald Trump, as long as he doesn't sucker punch anyone on stage or --

(CROSSTALK)

BURNETT: Are we going to hear "lying Ted" and "little Marco", or is he going to leave that at the door?

BROWNSTEIN: I don't think we know.

But I'm going to get both Ben and Amanda both -- isn't there a catch- 22? I mean, yes, you want it to be a two-man race for Ted Cruz. If it's a two-man race in Ohio and Florida, Ted Cruz is not going to be the winner.

CARPENTER: I wouldn't say that.

BROWNSTEIN: They need right now, they need these candidates to stop Trump from acquiring all those delegates in Ohio and Florida because if Kasich and Rubio fade, I do not see Ted Cruz beating Donald Trump in either of those states.

BURNETT: Final word, Amanda.

CARPENTER: But I would say Ted Cruz beat John Kasich in Michigan and people think that Ted Cruz is the alternative to Donald Trump, they're going to go with the winner.

BURNETT: We will see. People want to go with a winner. That's the one thing, they want to be -- they want to go for the winner. So, tonight, whoever emerges as a big winner could get a lot of momentum.

Thanks so much to all.

OUTFRONT next, Donald Trump, Ted Cruz, Marco Rubio, John Kasich, about to take that stage behind me right here at the University of Miami. The CNN Republican presidential debate just moments away. Stay with us.

(COMMERCIAL BREAK)

BURNETT: Donald Trump arriving here at the University of Miami. You can see him walking inside right here where I am getting ready for the Republican presidential debate. We saw Marco Rubio arrived with his wife Jeanette. Donald Trump here with his wife, and -- Melania, and also we have Ted Cruz also here. All of them here. Just waiting for John Kasich as we count you down to that crucial debate.